Systems on board airplanes (computers, screens, power electronics devices, valves, actuators, . . . ) are subjected to numerous vibratory phenomena, e.g. generated by the engines, the stream of air flowing over the airplane, and by running along the ground during takeoff and landing, to mention only a few examples. Throughout the present application, it should be understood that the vibratory phenomena may in particular be of an acoustic nature. These vibratory phenomena are heterogeneous in terms of frequency and amplitude and they depend on the stage of utilization or of flight (taxiing, takeoff, climbing, cruising, descending, landing, etc.), on air flow conditions (in-flight turbulence, etc.), and on the zones involved on board the airplane. Furthermore, systems of the “rotary machine” type (electric motors, fluid pumps, etc.) generate analogous vibratory phenomena that propagate through the airplane to other systems and to its structures, etc.
These vibratory phenomena are characterized by the type of the vibration (e.g. sinusoidal, random, transient), the associated spectra (in time and in frequency), resonance phenomena, etc. They have an impact on systems by reducing the lifetimes of mechanical parts, of electronics cards, of electronic components, and of structures, since the vibration subjects them to cycling and to fatigue. Amongst the effects that are induced thereby is a reduction in system reliability and an increase in preventative and/or corrective maintenance tasks.
A vibratory environment is characterized by its spectrum, which represents a parameter (amplitude, acceleration, etc.) as a function of the frequency of the signal. The spectrum may either be continuous, as applies to transient and random signals, or discontinuous or discrete as applies to harmonic or periodic signals, etc.
To mitigate vibration, attempts are made to absorb or to damp levels of vibration, which attempts consist in reducing the capacity of vibration to propagate and dissipate its energy. For this purpose, an absorber or damper presents a phenomenon of hysteresis in the dynamic elasticity relationship between stresses and strains. The vibratory environment may be improved by dissipating mechanical energy in three different ways, sometimes simultaneously.
It is possible to use a viscous fluid in which energy is dissipated in proportion to the speed of vibration, the fluid filling a reservoir in which a movable piston is immersed. However that dissipation gives rise to the suspension stiffening progressively with increasing frequency, where such stiffening can be compensated by installing the damper in series with high frequency decoupling.
In another known solution, friction is generated on a macroscopic scale by creating relative movement between the components of the structure under the effect of vibration. With friction, the amount of energy that is dissipated is proportional to the relative vibratory movement, but there exists a threshold effect. Under such circumstances, the system constitutes a significant source of non-linearities and is effective only at low frequencies with stresses presenting a large relative amplitude. When the threshold for initiating relative sliding between the elements is no longer reached, the elements allow vibratory stresses to pass through without being attenuated.
It is also possible to use the property of viscoelasticity, which is an intrinsic capacity of certain materials for dissipating vibratory energy. The dissipation of vibratory energy is then proportional to the vibratory acceleration. Under such circumstances, the molecular state of the material leads to its elasticity modulus and its shear modulus being represented mathematically in the form of complex numbers in which the real part corresponds to the elasticity of the material and the imaginary part represents its capacity for dissipation.
On board airplanes, the solutions presently implemented are based essentially on the following principles:                selecting locations for systems in zones that have acceptable levels of vibration. However these installation constraints are sometimes difficult to reconcile with other constraints, and they limit options in optimizing the design of the airplane and its systems;        adding mechanical parts to provide support and damping in a serial or parallel connection to provide passive control over the frequencies and the amplitudes of vibration on the systems. However such additional parts are often voluminous, they give rise to problems of aging over time, and they are sensitive to temperature, in particular when they are hybrid parts made both of rubber and of metal;        selecting components and assembly techniques that tolerate levels of vibration. However the resulting overdimensioning limits the options for optimizing systems installed on board an airplane; and        appropriate maintenance, but that has the potential of giving rise to higher operating costs.        
An object of the invention is to attenuate passively the levels of vibration on systems in order to improve their performance, lifetime, and maintenance.